The reactions of purified B and T cells to mitogens and antigens are being investigated. T cells from agammaglobulinemic chickens proliferate in response to mitogens and produce chemotactic factor. However, in humans both purified T and B cells were found to proliferate in response to appropriate stimulants and make chemotactic factors. These findings have been applied to study patients with periodontal disease. Their T as well as B cells have been found to proliferate and make mediators when stimulated by plaque antigens. These observations suggest a redefinition of the role of B cells in inflammation is required and needs further study.